Sanding sealers embodying polyvinyl butyral resins



Patented May 3, 1949 7 2,469,319 SANDING SEALERS EMBODYING POLYVINYLBUTYRAL RESINS Donald R. Swan, Berea, Ohio, assignor, by memoassignments, to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a.corporation of Pennsylvania N Drawing. Application February 15, 1946,Serial No. 648,012

6 Claims. (Cl. 260-23) This invention relates to coating materials andmore particularly to sanding sealers for use in finishing wood.

The customary procedure in the finishing of wood surfaces, such asfurniture, with lacquer involves first the application of a sandingsealer which should dry rapidly enough to permit sandlng within one hourwith dry sandpaper; this is followed with two coats of lacquer with oneor two hours between coats. The lacquer is frequently rubbed or polishedwith conventional rubbing materials to complete the finishing operatlon.

The function of a sanding sealer is to provide a suitable base orfoundation for the subsequen coats of lacquer. The sealer must dryquickly and when dry provide a surface which can be sandpapered withoutclogging the paper. The film provided by the sealer must build upsufficiently so that it may be sanded to provide a smooth level surface.-The film must be hard and firm enough to support the subsequent lacqueicoatings and prevent them from penetrating the wood. These qualities canbe obtained by conventional sanding sealers which ordinarilycomprisenitrocellulose lacquers embodying a hard, high melting resin, such asmaleic resin, having .a quick solvent release. Materials such as zincsoaps, with or without a minor proportion of magnesium carbonate andfinely divided soap stone, are frequently incorporated in sealers tomake the film more friable and thus improve the sanding properties. Suchsanding sealers, however, are unsatisfactory with respect to thedurability of the ultimate finish, for the reason that in order toobtain the required qualities of hardness, quick drying and easysanding, the toughness and elasticity of the sealers has beensacrificed, with the result that wood suriaces finished withconventional sealers and conventional lacquers are subject to marringand scratching and to failure under cold check tests. Heretofore, it hasbeen impossible to produce sanding sealers which embody the desiredsanding qualities and also the necessary toughness and adherencerequired to produce a durable mar resistant finish.

Accordingly, a general object 'of the present invention is the provisionof sanding sealers which have all of the desirable characteristics ofprior types of sealers in that they are quick drying and easy to sandand have the ability to hold out the subsequent lacquer coats, andwhich, in addition, are tough and adherent and thus furnish a strongbond between the lacquer and the underlying wood surface and improve thequality of the entire finish. Another object is the provision of sandingsealers having the above characteristics and which can be manufacturedeconomically. Another object is the provision resins may be used withgood results.

2 of sanding sealers which will maintain their toughness and elasticityfor long periods of time. Another object is the provision of lacquersanding sealers which will not adversely afiect the qualities oflacquers coated on them.

Briefly, the above and other objects and advantages of my invention areobtained by sealers embodying polyvinyl butyral resins of relatively lowviscosity with a suitable percentage of zinc stearate or the like toimprove the sanding characteristics. The polyvinyl butyral resins aredissolved in conventional solvents and may be used in conjunction withother film forming materials such as nitrocellulose, ethyl cellulose,cellulose acetate butyrate, and other acetals of polyvinyl alcohol suchas the acetaldehyde acetal of polyvinyl alcohol. So far as I am aware,polyvinyl butyral has never before been employed in the production ofsanding sealers. Probably the reason for this is that polyvinyl butyralresins in general are tough rather than hard, and have the quality ofretaining rather than quickly releasing solvents. Both of thesecharacteristics are seemingly antithetical to the qualities required ina sanding sealer, but contrary to expectations, I have found thatsanding sealers incorporating polyvinyl butyral resins in properconcentration dry quickly so that they may be sanded within an hour orless without any sign of clogging the sandpaper. They are hard and firmenough to support the finishing coats prop-' erly and in addition theirtoughness and adhesiveness is such that the entire finishing system isof greater durability and has better resistance to, marring orscratching than systems obtainable with prior types of sanding sealersand the same lacquers. Preferably, I employ polyvinyl butyral of lowviscosity, although by proper blending with other resins, high viscosityBy low viscosity resins I mean resins made from polyvinyl acetate havinga viscosity of 10 centipoises or less in solution in benzene at aconcentration of 86 grams per liter at 20 C. Viscosities of polyvinylacetate referred to hereinafter are on this basis, and are indicated byV followed by a numeral corresponding to the viscosity.

The following are examples of sanding sealers embodying my invention.These examples are given by way of illustration only and not by way oflimitation.

EXAMPLE 1.A SANDING SEALER EMBODYING A Low VISCOSITY PoLYvmYL BU'rYmu.Rssm A. Preparation of butyral resin A solution was prepared containing1'72 grams polyvinyl acetate (V-7) in 1000 cc. of percent ethyl alcohol.To this solution was added (with stirring) 60 cc. oi concentratedhydrochloric aol followed by 72 grams of butyraldehyde.

The mixture was allowed to react for 48 hours at 50" C. The solution wasthen diluted with three liters of 95 percent ethyl alcohol and thepolyvinyl butyral precipitated by pouring into water. After washingsubstantially free of contaminants the fibrous product was air-dried forseveral days.

B. Preparation of sanding sealer Polyvinyl butyral g 7.8 Zinc stearate g0.7 sec. nitrocellulose g 0.7 Butyl acetate cc 19.0 Methyl acetone cc40.0 Methyl ethyl ketone cc 3.0 Toluene cc 3.0

One coat of this composition was sprayed on a gumwood panel. After /2hour it was possible to sand the panel without drag and without pickingup any of the coating on the sandpaper as a gummy deposit. Two coats ofa conventional furniture rubbing lacquer (nitrocellulose, hard resin andplasticizer) were then applied by spraying.

After one month, the lacquer-sealer system was compared with a standardsystem embodying the same lacquer and a conventional sanding sealer. Theexperimental system was very much tougher and more mar resistant thanthe standard.

A sanding sealer made as described above is very satisfactory, but thewashing and drying of the low viscosity polyvinyl butyral is difficulteven under laboratory conditions. Accordingly, in the absence ofcommercially available low viscosity polyvinyl butyrals, I prefer toemploy various other materials in combination with the butyral. Forexample, I may employ a co-precipitate of polyvinyl butyral and acellulose derivative produced in accordance with the disclosure of mycopending application Serial No. 648,011, filed of even date herewith,for Low viscosity polyvinyl butyral resins and methods of making same.Such a sealer is described in the immediately following example:

EXAMPLE 2.-A SANDING SEALER EMBODYING Low VIscosrrY POLYVINYL BUTYRALAND A CELLULOSE DERIVATIVE A. Preparation of butyral resin The followingwere mixed in a glass vessel:

Polyvinyl acetate (V-7) .g 1'72 95% ethyl'alc cc 600 Butyraldehyde cc 80Hydrochloric acid (sp. g. 1.18) cc 50 of sodium hydroxide (sufficient toneutralize the hydrochloric acid) The supernatant liquid was then pouredoff thus removing some of the contaminants.

The residual mass of soft resin was then taken up in about 1 liter of 95percent ethyl alcohol containing about 5 percent of butyl cellosolve(C4H9.O.CH2.CH2OH) which was added to obtain complete solution of theresin. One hundred grams of V4-second' nitrocellulose (65 grams dryweight) dissolved in 500 cc. of acetone was then mixed with the butyralsolution.

The resulting solution was poured into a stream of water, resulting in awhite, fibrous precipitate which was easy to wash and dry withoutagglomeration. The yield was 184 grams of air-dried material.Approximately 65 grams or 35 percent of this was cellulose nitrate.

B. Preparation of sanding sealer Ten grams of the above co-precipitated'material was dissolved in cc. of solvent. To this solution was added 1:5cc. of a dispersion of zinc stearate in cellulose nitrate solution.

The final composition was as follows:

This composition, which contains about 12 percent of solids by weight,was sprayed without difilculty onto a gumwood panel. After drying forhour, the panel was sanded readily without any drag or gu'mming of thesandpaper. The wood panel was then finished with two coats of the sameconventional nitrocellulose furniture rubbing lacquer used in theprevious example, and tests after 60 days indicated that the entirefinish system was much tougher and had greater resistance to marringthan a similar panel finished with a conventional sanding sealer and twocoats of the same lacquer.

Sanding sealers may also be produced from co-precipitates of polyvinylbutyral and ethyl cellulose and of polyvinyl butyral and celluloseacetate butyrate, such as the co-precipitates described in Examples 4and 5 of my aforesaid copending application, using appropriateproportions of solvents to give the desired viscosity.

Exzmrm 3.A SANDING SEALER Emonyme If Com- MERCIALLY AVAILABLE POLYVINYLBU'rYnAI.

The following were placed in a pebble mill and ground for 18 hours:

Polyvinyl butyral VF-4100 g..

Zinc stearate g 3.39 Ethyl acetate cc 590.00 Butyl acetate cc 295.00Ethyl alcohol (denatured) cc 295.00

the sealer-lacquer system as compared to a standard system.

Polyvinyl butyral VF-4l00 is manufactured by E. I. du Pont de Nemours 8:Company and is a polyvinyl butyral resin having a viscosity of 40 cp. in95 percent ethyl alcohol at a concentration of 5 percent by weight at atemperature of 80 F. and containing about 10 percent of unreacted vinylalcohol groups.

EXAMPLE 4.A SANDING SEALER EMBODYING THE SAME POLYVINYL BurYRAL UsED inEXAMPLE 3 AND AN ACETALDEHYDE ACETAL or- POLYVINYL ALCOHOL The followingmaterials were ground for 12 hours in a pebble mill:

Polyvinyl acetal of acetaldehyde made from polyvinyl acetate (V-5) g150.4 Polyvinyl butyral VF-4l00 g 49.6 Zinc stearate suspended innitro-cellulose solution g 15.9 Toluene cc 946.0 ethyl alcohol cc 592.0Ethyl acetate cc 148.0

The resulting mixture was thinned to spraying viscosity with 1950 cc. ofa thinner composed of the following:

Parts by volume Ethyl acetate 5.0 Butyl acetate 22. 95% ethyl alcohol10.0 Butanol 7.5

Toluol 55.0

The sealer gives very good results, spraying readily at reasonableconcentrations of solids; in this respect it is superior to the sealerof Example 3. The sprayed coating may be sanded without drag or gummingof the sandpaper, and tests after aging indicate that a system offinishing materials embodying this sealer and two coats of the sameconventional nitrocellulose furniture rubbing lacquer used in previoustests is much superior, insofar as toughness, resistance to marring anddurability, are concerned, to a system embodying two coats of the samelacquer over a conventional sanding sealer.

EXAMPLE 5.-A SANDING SEALER EMBODYING A MIXED POLYVINYL AcErAL orBUTYRALDEHYDE AND AcE'rALDEHYDE (REFERRED TO HEREINAFTER AsBUTYRACETAL), AND MADE WITHOUT ISOLAT- mc THE RESINS .Sanding sealers ofthis type are disclosed and specifically claimed in my copendingapplication Serial No. 648,013 filed of even date herewith for Coatingcompositions embodying polyvinyl but'yral resins and methods of makingthe same. One such sealer may be produced as follows:

The following ingredients were mixed in the order indicated and reactedduring two days at 50 C. with occasional stirring:

Polyvinyl alcohol of 5 cp. viscosity in 4% by weight solution in waterat C, g 264 95% ethyl alcohol cc 1500 Sulfuric acid (sp. g. 1.84) cc 10Butyraldehyde (97.2 g.) cc 120 Paraldehyde (59.4 g.) cc 60 The resultingthick, somewhat hazy dope was neutralized with 181 cc. of a solutionmade by dissolving 100 grams sodium hydroxide in 1 liter of ethylalcohol. The resulting solution had a pH of about 7.

Solvents were then added as follows to facilitate filtering and toprovide suitable consistency for spraying:

- Toluene l 1 cc 1600 Methyl ethyl ketone cc 900 Petroleum naphtha (B.P. 93-112 C.) cc 500 The solution was filtered with pressure throughpaper to remove sodium sulfate and gel particles.

Zinc stearate (21 grams) was ground into 3525 cc. of the solution and87.5 grams of /2-second nitrocellulose was added. This amount ofnitrocellulose improves the sanding qualities and does not detractgreatly from the toughness of the final system.

The resulting sanding sealer consists of the following:

Polyvinyl Butyracetal g 262.0

-sec. nitrocellulose (65%) (50 g. dry wt.) 87.5 Zinc stearate (6.7% ofvehicle solids) g 21.0 95% ethyl alcohol cc 1500.0 Toluol cc 1600.0Petroleum naphtha (B. P. 93-112 C.) cc 500.0 Methyl ethyl ketone cc900.0

When sprayed on wood the composition dried quickly and was sanded after/2 hour without drag or gumming. When two coats of the same clearlacquer as used in previous tests were applied over the sealer, hold-outwas equivalent to conventional sealers. Comparative tests of thesealer-lacquer system showed much greater toughness than a standardsystem embodying a conventional sealer and the same lacquer.

Sanding sealers made according to the above examples all have thecharacteristics of drying so that they may be sanded within an hourafter spraying, of being easily sanded to a smooth surface without dragor gumming of the sandpaper, of being compatible with ordinarynitrocellulose lacquers and holding-out succeeding lacquer coats, and ofbeing tough and adherent so that a finish system embodying one of thesanding sealers of the present invention and a conventional lacquer issuperior to a system embodying the same lacquer and a conventionalsanding sealer, with respect to toughness, adherence, durability,resistance to marring and scratching and when subjected to cold checktests.

The foregoing examples show that butyral resins may be used successfullyin sanding sealers of various formulations and in combination withvarious other resins and the like. However, in order to secure propertoughness and adhesion, I prefer that not less than 50 percent of thefilm forming material content be polyvinyl butyral. Where polyvinylbutyral resins are used without substantial quantities of other filmformers, it is preferable to use polyvinyl butyrals of low viscosity, i.e., having viscosities corresponding to the viscosity of polyvinylbutyrals made from polyvinyl acetate having a viscosity of 10 cp. orless, and preferably about 7 cp. Also if polyvinyl butyrals made frompolyvinyl acetate having a viscosity of less than about 4 cp. areemployed. it is desirable to blend them with higher viscosity butyralssuch as those made from polyvinyl acetate having a viscosity of about atleast 6 cp. in order to prevent the sealer from being too brittle. It isalso desirable to employ resins in which the hydroxyl content, aspolyvinyl alcohol, does not exceed about 22 percent. Such resins cantolerate more modifying agents, such as cellulose derivatives, and otherpolyvinyl acetals while retaining the desired characteristic ofpolyvinyl butyral,

than resins of greater hydroxyl content. In order to obtain good sandingqualities it is desirable that a material such as zinc stearate or othersuitable agent be incorporated in the sealers to make the films morefriable; also the sealers must not contain substantial quantities of anymaterial, such as shellac, which will gum or clog the sandpaper. In theprior art it has always been taught that maleic-rosin resins must bepresent to obtain good solvent release. However, I have found that nosubstantial amount of maleic resins can be tolerated in butyral sealersbecause such maleic resins immediately cause loss of toughness.

fled to obtain various characteristics in the seal- The formulations setforth above may be modi- I ers, and various other changes andmodifications prising an organic solvent, a major portion of the solidscontent of said sealer being a polyvinyl butyral resin having theviscosity of a polyvinyl butyral resin made from polyvinyl acetatehaving a viscosity of not more than 10 centipoises at C. in a solutionin benzene containing 86 grams per liter, said sealer containingsubstantially no shellac and substantially no malelc resin, said sealercontaining zinc stearate in the amount of not more than 10 percent ofthe solids content thereof, and said sealer drying sufliciently rapidlyto permit sanding within one hour after spraying without drag'or gummingof the sandpaper.

2. A sanding sealer'ac'cording to claim 1 wherein the total solidscontent of the sealer at spraying viscosity is at least 7 percent byweight.

3, A sanding sealer according to claim 1 in which the solids contentcomprises a co-precipiv 8 tate of low viscosity polyvinyl butyral and acellulose derivative from the group consisting of cellulose nitrate,cellulose acetate butyrate and ethyl cellulose and mixtures thereof.

4. A sanding sealer particularly adapted for application to woodsurfaces preparatory to the application of lacquer thereto, said sealercomprising an organic solvent a major portion of the solids content ofsaid sealer being a mixtue oi acetals of polyvinyl alcohol one of whichis polyvinyl butyral, said sealer containing a small percentage but notmore than 10 percent of zinc stearate.

5. A sanding sealer according to claim 4 wherein the weight of polyvinylbutyral is at least half the total weight of acetals of polyvinylalcohol present.

6. A sanding sealer particularly adapted for application to woodsurfaces preparatory to the application of lacquer thereto, said sealercomprising an organic solvent, the resin content of said sealercomprising polyvinyl butyral and the acetaidehyde acetal of polyv ylalcohol, said sealer containing a small percentage but not more than 10percent of zinc stearate.

DONALD R. SWAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,293,558 overholt Aug. 18, 1942FOREIGN PATENTS Number Country Date 872,647 Great Britain May 12, 1932483,222 Great Britain Apr. 8, 1938 OTHER REFERENCES Page 637, J. JMatiello, Protective and Decorative Coatings, vol. II, John Wiley 8:Sons, New York, 1942. (Copy in Division 50.)

